Influences of probe shape and surface roughness on tack properties measured by the probe tack test and characterization of crosslinked polyacrylic pressure‐sensitive adhesives

For a probe tack test for a pressure‐sensitive adhesive (PSA) under the conditions of light contact pressure and short contact time, probes with shapes and surface roughnesses suitable to achieve better wettability were investigated. A smooth, polished probe that became slightly convex at its center was found to be superior to flat‐ended. High surface roughness decreased tack. Debonding observations showed that fibrillation started from the probe edge and extended to the center. The fibril grew, without peeling, until the peak of the force–displacement curve was reached. After the peak, the fibril growth and peeling advanced simultaneously. The fibrillation was important to tack development. The test conditions necessary to observe the deformation behavior of PSA tape with sufficient interfacial adhesion were investigated. The system was preheated at 60°C for 1 h after the probe and PSA tape contacted each other, and was then cooled. The PSA performance of crosslinked random copolymers poly(n‐butyl acrylate‐acrylic acid) (A) and poly(2‐ethylhexyl acrylate‐acrylic acid) (B) were compared. A shoulder formed by fibrillation after the peak in the force–displacement curve was observed only for B. Copolymer B exhibited better interfacial adhesion and deformability. The preheating method was found to be useful for characterizing PSAs. Which probe is suitable for better wetting?